servo

A stroke is caused when poor blood flow to the brain causes cell damage, causing that part of the brain to stop functioning. Common causes are either blood vessel blockage or internal bleeding, and effects depend on the part of the brain that is affected. In most cases, spasticity (muscle contraction), poor motor control and the inability to move and feel are common after effects. Recovery is often a long, slow process and involves re-learning the affected lost skills. This is where physical therapy using assistive technologies becomes important. Rehabilitation must start as early as possible since the first few weeks are critical for good recovery. [Sergei V. Bogdanov] is building a cheap and simple Post-Stroke Spasticity Rehab Helper to address this problem.

He’s using ten hobby micro servos connected to an Arduino Nano, all mounted on a kitchen chopping board, with a few other bits thrown in to round out the build. There’s one pair of servos for each finger. A five bar linkage converts the servo rotations to two-dimensional motion. The end of the linkage has a swiveling metallic disk. Patient fingers are attached to these discs via magnetic metal pads that are attached to the end of the fingers using adhesive plaster tape. Two push buttons cycle through a large number of exercise modes and two potentiometer’s help adjust the speed and smoothness (the number of points calculated for the desired motion). Two 7-segment LED display modules connected to the Arduino provides a visual interface showing program modes, speed, number of cycles and other relevant information. Replicating the project ought to be very straightforward since the device uses off-the-shelf parts which are easy to put together using the detailed build instructions, photos and code posted on [Sergei]’s project page. Check out the videos below to see the rehab helper in action.

Hackaday gets results! Reader [John] saw our recent Fail of the Week post about a “sand matrix printer” and decided to share his own version, a sand-dispensing dot matrix printer he built last year.

Granted, [John]’s version is almost the exact opposite of [Vjie Miller]’s failed build, which sought to make depressions in the sand to print characters. [John]’s Sandscript takes a hopper full of dry, clean sand and dispenses small piles from six small servo-controlled nozzles. The hopper is mounted on a wheeled frame, and an optical encoder on one wheel senses forward motion to determine when to open each nozzle. As [John] slowly walks behind and to the side of the cart, a line of verse is slowly drizzled out onto the pavement. See it in action in the video below.

More performance art piece than anything else, we can see how this would be really engaging, with people following along like kids after the [Pied Piper], waiting to find out what the full message is. There’s probably a statement in there about the impermanence of art and the fleeting nature of existence, but we just think it’s a really cool build.

Internals of 3D printed “print and fold” robot. [Image source: MIT CSAIL]Robot design traditionally separates the body geometry from the mechanics of the gait, but they both have a profound effect upon one another. What if you could play with both at once, and crank out useful prototypes cheaply using just about any old 3D printer? That’s where Interactive Robogami comes in. It’s a tool from MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) that aims to let people design, simulate, and then build simple robots with a “3D print, then fold” approach. The idea behind the system is partly to take advantage of the rapid prototyping afforded by 3D printers, but mainly it’s to change how the design work is done.

To make a robot, the body geometry and limb design are all done and simulated in the Robogami tool, where different combinations can have a wild effect on locomotion. Once a design is chosen, the end result is a 3D printable flat pack which is then assembled into the final form with a power supply, Arduino, and servo motors.

A white paper is available online and a demonstration video is embedded below. It’s debatable whether these devices on their own qualify as “robots” since they have no sensors, but as a tool to quickly prototype robot body geometries and gaits it’s an excitingly clever idea.

Is this a case of a good design gone wrong in the build phase? Or is this DIY prosthetic arm a poor design from the get-go? Either way, [Will Donaldson] needs some feedback, and Hackaday is just the right place for that.

Up front, we’ll say kudos to [Will] for having the guts to post a build that’s less than successful. And we’ll stipulate that when it comes to fully articulated prosthetic hands, it’s easy to fail. His design is ambitious, with an opposable thumb, fingers with three phalanges each, a ball and socket wrist, and internal servos driving everything. It’s also aesthetically pleasing, with a little bit of an I, Robot meets Stormtrooper look.

But [Will]’s build was plagued with print problems from the start, possibly due to the complex nature of the bosses and guides within the palm for all the finger servos. Bad prints led to creaky joints and broken servos. The servos themselves were a source of consternation, modified as they were for continuous rotation and broken apart for remotely mounting their pots in the hand’s knuckles. The video below relates the tale of woe.

Every good dog is deserving of a treat. [Eliasbakken]’s dog [Moby] is a certified good boy, so he designed a dispenser with a touchscreen that his dog can boop to treat himself when he isn’t barking up a ruckus.

Adding a touchscreen to a treat dispenser when a button would suffice is a little overkill, but we’re not here to judge. [Eliasbakken] is using a BeagleBone Black — a Linux-based development platform — as this dispenser’s brains, and a Manga touchscreen that is likely to see a lot of use. A wood-like material called Vachromat was laser cut for the frame and glued together, while an RC servo with a 3D-printed jointed pushing arm to dispenses the treats. The dispenser’s hopper only holds fifteen, so we expect it will need to be refilled every fifteen seconds or so.

At least one in their lives — or several times a day — everyone has wished they had a third hand to help them with a given task. Adding a mechanical extra arm to one’s outfit is a big step, so it might make sense to smart small, and first add an extra thumb to your hand.

This is not a prosthetic in the traditional sense, but a wearable human augmentation envisioned by [Dani Clode], a master’s student at London’s Royal College of Art. The thumb is 3D-printed out of Ninjaflex and mounted to a printed brace which slides over the hand. One servo rotates the thumb, and a second pulls it closed using a bowden cable system — not unlike that of a bicycle brake. Control of the thumb is achieved by pressure sensors in the wearer’s shoes, linked via Bluetooth to a wristband hosting the servos and the electronics. We already use our hands and feet in conjunction, so why not capitalize on this intuitive link?

A few years ago, [patchartrand] decided to build a robot arm. The specs were simple: he needed a drive system that would be at least as strong as a human arm. After looking at motors, [patch] couldn’t find a solution for under $3,000. This led to the creation of the Ultra Servo, an embiggened version of the standard hobby servo that provides more than ten thousand oz-in of torque.

Your typical hobby servo has three main components. The electronics board reads some sort of signal to control a motor. This motor is strapped into a gear train of some sort, and a potentiometer reads the absolute position of a shaft. This is basically what the Ultra Servo is doing, although everything is much, much bigger.

The motor used in the Ultra Servo is a very large brushed DC motor. This is attached to a 160:1 planetary gearbox and the electronics are built around four reasonably large MOSFETs. The electronics are built around the ATmega168 microcontroller, and the specs for the completed servo include 12 V or 24 V operation, TTL, SPI, and standard RC communication, 60 RPM no load speed, and 60 ft-lbs of torque.

This is not your standard servo. This is a massive chunk of metal to move stuff. If you’ve ever wanted a remote-controlled Cessna, here you go. That said, servos of this size and power will always be pricey, and [patch] is looking at a cost of $750 per unit. Still, that’s much less than the thousands of a comparable unit, and a great entry to the Hackaday Prize.